JPS6276072A - Index servo system - Google Patents

Abstract

PURPOSE:To position accurately a magnetic head by imbedding servo information to plural parts of an index area and obtaining position information from each of the servo information respectively. CONSTITUTION:In the index area 3, >=3 sets of servo information SD1, SD2,... are imbedded in series in the circumferential direction of a disc. The period of the servo information SD1, SD2,... is imbedded so as to be longer than the sum of the charging time of peak hold circuits 11a, 11b applying peak hold to bit cells A, B and the time applying A/D conversion to the position signal and fetching the result in a microprocessor 14. The microprocessor 14 obtains an off-track quantity delta of a magnetic head 4 from the position information to control the drive current of the phases A, B of a step motor 17 via D/A converters 15a, 15b and current drivers 16a, 16b. The step motor 17 drives a carriage 18 to move a magnetic head 4 fitted to the carriage 18.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an index servo method for positioning a head using servo information embedded in an index area of a magnetic disk.

[Technical background of the invention and its problems]

Conventionally, in the field of small magnetic disk drives, an oven loop positioning system using a stepper motor, which has a simple magnetic head positioning mechanism, has been used exclusively. However, with this positioning method, positioning accuracy is determined only by the feed accuracy of the stepper motor, resulting in large thermal off-tracks and making it difficult to increase track density.

Therefore, an embedded servo method has been proposed in which servo information for head positioning is embedded in a part of the area where data is written so that the head can be accurately positioned even at high track densities. This embedded servo method is divided into sector servo method, which divides the disk into multiple sectors and embeds servo information in each sector, and index servo method, which embeds servo information in only one place per revolution of the disk. Broadly classified.

The former has multiple pieces of servo information, so it can track not only thermal off-track but also eccentricity. Therefore, it is suitable for a medium exchange type disk device.

However, in this method, servo information is embedded in each sector, so formatting cannot be performed by connecting to a soft sector interface.

Therefore, there was a drawback that existing controllers could not be used.

On the other hand, the index servo method has the disadvantage that it cannot follow the eccentricity of the disk because the servo information is formed only in the index area of the disk, but it is suitable for most types of small magnetic disk drives that do not require replacing the disk. In the field of fixed magnetic disks, which are currently the dominant field, advantages include high-density positioning by eliminating thermal off-track, and the ability to format soft sectors using existing controllers.

For this reason, various index servo systems described below have been proposed and put into practical use.

5VQuest's Digilock servo system (Nikkei Electronics, 1983). 7.18, variable length sector 3
．． The embedded servo method for 9-inch disks is a method in which two burst-shaped servo patterns A and B are embedded diagonally in the index area over four tracks. Position information can be obtained by binarizing the signal waveform read from the servo pattern at an appropriate level and calculating the difference between the pulses obtained from the left and right sides of the servo pattern. Therefore, since it does not include circuits for analog averaging or peak holding of position signals, it has the advantage of simplifying the electrical circuit. However, the biggest drawback of this method is that the servo pattern must be written diagonally over four tracks because the position is expressed by the number of pulses. In this case, it is necessary to write the pattern by gradually shifting the track pitch by an amount equal to this division pitch by an additional several tens of minutes. Therefore, the time required to write a servo pattern is several tens of times longer than the conventional writing time for each track. If this writing time is to be shortened, the number of pulses must be reduced, leading to a deterioration in position detection accuracy. Furthermore, this servo pattern also has the disadvantage that if there is a defect in a part of the pattern, it cannot be detected and this defect appears as a positioning error.

Therefore, an index servo method has been proposed in which two burst patterns A and B are arranged alternately every other track, and these patterns are shifted by half a trunk pitch with respect to the data track (Mitsubishi Electric Technical Report Vo, 59.N.

4.1985. p 57-60). This pattern is based on the sector servo method (Q riVetec, fvlini
-1icro systemsJuly 1983
．． Half-1+eight m1nirloppy
5tores3.3Mbyjes). In this method, two signals A and B from the magnetic head are averaged by full-wave rectification/C, and the difference between A and 3 is taken as a position signal.

However, since averaging is not sufficient in this method, if there is a defect in the servo pattern, it will appear as a positioning error. In order to eliminate this problem, one possible method is to extract multiple A and B difference signals and average them, but in order to achieve this in a small servo area, a high-speed A/'D changer is required. Since the signal waveform obtained from the servo pattern differs between the inner and outer circumferences of the disk, this method of full-wave rectification and then averaging makes the circuit expensive. Another drawback was that a large error occurred in the position signal between the inner and outer circumferences of the disk.

[Purpose of the invention]

The present invention improves the drawbacks of the conventional index servo system described above, and aims to provide an index servo system that is inexpensive and has high positioning accuracy by devising the shape of the servo pattern.

(Summary of the Invention) The present invention forms an index area in a part of the recording RR of a magnetic disk, uses the other part as a data area, and uses servo information embedded in the index area to position the magnetic head. In the index servo method, the servo information is shifted by half a track pitch with respect to the tracks formed in the data area, and the servo information is distributed at least three times in the circumferential direction of the index area.
When the dispersion of each positional information obtained from each of these servo information is smaller than a preset value, the off l-rack control for the track is determined based on the average value of all the obtained positional information. Also, if the dispersion of the position information obtained from the index area is larger than a preset value, the off-track rank of the relevant truck is determined by excluding position information that deviates from the predetermined range, and these obtained off-track positions are It is characterized in that the magnetic head is positioned based on the track position.

〔Effect of the invention〕

According to the present invention, servo information is embedded in multiple locations in the index area, and position information is obtained from each of these servo information, so there may be defects or noise in the servo information. However, burst-like errors are less likely to occur, and the probability that all position information is affected by noise is low. Further, since abnormal position information is identified from the position information and removed to determine off-track suspension, accurate positioning of the magnetic head can be performed.

Furthermore, in the present invention, since the servo information including the position information is stopped independently, there is sufficient time to detect the next position information from one piece of position information. Therefore, there is no need for a high-speed D/'D converter, and it can contribute to reducing the cost of the circuit.

Further, in the present invention, since the servo information is shifted by a half track bit from the data track, there is an advantage that writing of the servo pattern for one track only needs to be done once.

Example C) An example of the present invention will be described below with reference to the drawings.

In FIG. 1, a magnetic disk 1 has a data area 2.
An index area 3 is formed by deleting a part of this data area 2 in the circumferential direction, and these data areas 2 and index areas 3 form a recording area. Index area 3 contains three or more servo information SD+.

SD2. ... are embedded in series in the circumferential direction of the disk. Each servo information SC)+, SD2,...
. each consists of a synchronization section CI, an erasure section E, a synchronization section C2, and a position information section PD. Synchronization part C+,
C2 is provided in order to detect the erasing section E.
The settings are convenient for importing into the PU. The rear of the synchronizing parts C+ and C2, especially the latter synchronizing part C2, can also be used to create an AGC (auto gain control) voltage. The erasing section E is the location information cell A.
, B serves as a reference for creating signals necessary for servo decoding, such as a hold signal that provides the timing for peak holding. In the position information section PD, position information consisting of two position bit cells in a dibit configuration are alternately embedded and shifted by half a track with respect to the data track.

These servo information SOs, SC2, . . . are written by a device called a servo writer, for example, in synchronization with an index signal to be described later. In this case, with a magnetic head whose track width is wider than the track pitch of the servo pattern,
Overwritten. Therefore, as shown in FIG. 1, the position information cell has a shape written over the entire track pitch.

In FIG. 2, the magnetic head 4 is the PI in FIG.

This shows the respective signal forms at positions P2 and P3. In the case of Pl in which the magnetic head is off-track to the n+1 track side, P1 to Cell A has the maximum amplitude, and P1 to Cell B has the minimum amplitude. In the case of P2, when the magnetic head 4 is on track on the n track, both the cells A and B have an intermediate level amplitude. In the case of P3 in which the magnetic/rad 4 is off-track to the n-1 track side, bit cell A has the minimum amplitude and bit cell B has the maximum amplitude.

After peak-holding these position information cells A and B, the difference between them is taken as a position signal (A-8>).The level of the above position signal relative to the position of the magnetic head 4 is shown in FIG. If the magnetic head is on the slope of the position signal, the off-track distance can be determined from the level of the position signal.Assume that the magnetic head is at the position Xl.The track width is TW, and the track width is TW. If the pitch is Tp, the maximum value of the position signal is emax, and the level of the position signal at point X1 is el, then the off-track value δ of the magnetic head is δ= (e1/2emax) −Tw ・(
It can be expressed as 1).

That is, if the level of the position signal obtained from the servo area is el when the magnetic head is sent to the n-th track, then the off-track angle δ is expressed by equation (1).

Therefore, in order to bring the magnetic head onto the n-th track, it is sufficient to change the balance of the currents flowing through the A phase and B phase of the stepper motor so that e1=0. Note that the polarity of the position signal is different for even-numbered tracks and for several tracks.

In the present invention, the position signal as shown in FIG.
It is designed so that it can be obtained from three or more locations.

This is because if there is only one piece of position information, if the position information happens to be lost due to a defect in the disk, positioning on that track will not be possible.

Furthermore, by averaging a plurality of pieces of position information, the accuracy of the position information can be increased and resistance to noise can be increased. Therefore, the more positional information there is, the better it is for the above purpose, but on the other hand, it requires a larger servo area. Therefore, 3 to 5 are selected practically. When the position signal S, 'N is bad, it is 5
servo information may be used.

FIG. 4 shows the configuration of a magnetic head positioning device when using a magnetic disk in which the above-mentioned servo information is embedded.

A signal read from the magnetic head 4 is amplified by an amplifier circuit 6 and then sent to an AGC voltage generation circuit 7, a binarization circuit 8, peak hold circuits 11a and 11b, and a data R/W circuit (not shown).

The AGC voltage generated by the AGC voltage generation circuit 7 is used for gain control of the amplifier 6.

The signal binarized by the binarization circuit 8 is sent to the erased portion detection circuit 9. The erasing section detection circuit 9 is composed of, for example, a retriggerable mono multivibrator, and has a 2fli
The longest zero level portion of the eraser signal pulse is detected and an eraser detection signal is output. As shown in FIG. 5, eraser detection signals are obtained as many times as there are servo information pieces. This eraser detection signal becomes a reference signal for servo decoding, and the rise of this signal is used to generate a hold signal, a hold clear signal, an A/D conversion signal, and an A/D conversion signal for the position signal shown in FIG.
Various signals such as a gain signal and an R/"vV index signal are generated. These signals are generated by the timing pulse generation circuit 10. The index signal is a signal obtained in synchronization with the rotation of the motor and is generated in the servo area. represents the start of.

The peak hold circuits 11a and 11b store the bit cell A of position information based on the peak hold signal.

Hold each peak of B. The differential amplifier 12 takes the difference between these peak held position information and outputs it as a position signal. At this time, the position signal is a positive signal obtained by adding an offset of e max to the signal in FIG. 3 to facilitate A/D conversion. There are multiple position signals, which are sequentially A/D converted by the Δ/D converter 13.
It is loaded into the microprocessor 14. Therefore, the servo information SD1. The period of SD2, . . . is determined by the peak hold circuit 11a that peak-holds the bit cells A and B.
.

11b and the time required to convert the position signal into A, . . . 'D and input it into the microprocessor 14.

The microprocessor 14 determines the off-track amount δ of the magnetic head 4 from the position information, and calculates the off-track amount δ of the magnetic head 4, and
5b and current driver 16a.

A-phase and B-phase drive currents of the stepper motor 17 are controlled via the stepper motor 16b. The stepper motor 17 drives a carriage 18 to move the magnetic head 4 attached to the carriage 18.

Next, the variation processing in the microprocessor 14 will be explained, taking as an example the case where there are four pieces of position information embedded in the servo area.

Each location information is al, a2. a3. aq (O~2 each
eIIlax). A tolerance value for variation in position information is set in advance to bo. The positional deviation amount δ0 corresponding to this is δa − (bo, '2emax) ・7w −(
It can be expressed as 2). The value of b is S/N, intrusion noise,
The defect level is determined by considering the allowable positioning error, etc., but is generally selected to be around 10% of 2emax.

In order to remove as much defects and noise as possible from the position information, the following processing is performed.

First, among the four location information, the maximum value ap and the minimum value aq
is removed, and the average value m2 of the remaining two pieces of position information is taken.

<i=1.2, 3.4) Next, find 1m2-al 1 and check whether it is within half ba/2 of the allowable variation value, that is, bo/2 1
m2 at I≧O・(41 discrimination is f:T now.

■ All four location information (al,..., a4) are (
4) If the formula is satisfied, all position information is normal, so take the average of the four position information and mD-Σa I/4
.=(5) Let this be the position information in the servo area.

The corresponding off-track amount δ is δ = (no / 2 emax)
-Tw・f6). The microprocessor 14 changes the current balance of the A-phase and B-phase of the stepper motor 17 via the D/A converters 15a and 15b so that the off-track amount δ becomes zero.

■ If one of the four pieces of position information does not satisfy equation (4) above, it is assumed that one of the four pieces of position information has a defect or intrusion noise, and satisfies equation (4). Delete the location information ap that did not. The average of the remaining three pieces of position information is taken as the correct position information.

Then, the off-track amount δ, which is the same as (2), is determined, and the phase current of the stepper motor 17 is changed so that this off-track Hδ becomes zero.

■ If two of the four pieces of position information do not satisfy equation (4) above, two of the four pieces of position information (ap, aq
) is assumed to have a defect or intrusion noise. In this case, since the two except ap and a'q are normal, their average value m2 is determined by equation (3). Then, similarly to ■, find the off-track amount δ, and this off-track amount δ
The phase current of the stepper motor 17 is changed so that the current becomes zero.

■ If three or more of the four pieces of position information do not satisfy equation (4), there are two or more defects or intrusive noises among the four pieces of position information. This is a case where the average value is sandwiched between two pairs of position information, unlike in ■, even if the two pieces are the same. In these cases, it is difficult to determine the normal level of location information. Therefore, the position information obtained by 1q from the servo area is regarded as defective, and the phase current balance of the stepper motor 17 is not changed.

In this way, according to this embodiment, even if there is a defect in the servo information, an accurate amount of off-track can be determined. In this case, peak-hold the two Got Cells A and B, find the difference between them, and obtain position information.
Since the obtained position information is normalized by 2e max to obtain the off-track amount, it is possible to obtain an accurate off-track amount even if the read waveform changes at the inner and outer circumferences of the disk.

The above is a case in which there are four pieces of position information, but even in the case of a plurality of ponds, processing can be similarly performed in accordance with variations in position information.

[BRIEF DESCRIPTION OF THE DRAWINGS] FIG. 1 is a diagram showing a magnetic disk and its servo pattern used in an index servo system according to an embodiment of the present invention, and FIG. 2 is a diagram showing the position of a magnetic head and its readout waveform. FIG. 3 is a waveform diagram showing the relationship between the position of the magnetic head and the position signal; FIG. 4 is a block diagram of a device for implementing the index servo system using the magnetic disk; FIG. The figure is a timing diagram showing each signal generated by the device. 1...Magnetic disk, 2...Data area, 3...
・Index area, 4...magnetic head, SDt
. SD2... Servo information, Ct, C2... Same part,
E...Erasing section, PD...Position information section. Applicant's representative Patent attorney Takehiko Suzue No. 1 Figure 2 Figure 3 AGC

Claims (5)

[Claims] (1) An index area is formed in a part of the recording area of the magnetic disk, and the other part is used as a data area,
In an index servo method in which magnetic head positioning is performed using servo information embedded in the index area, the servo information is distributed in the circumferential direction of the index area by shifting by a half track pitch with respect to the tracks formed in the data area. It is embedded in at least three locations, and when the dispersion of each positional information obtained from each of these servo information is smaller than a preset value, off-track on the relevant track is determined based on the average value of all the obtained positional information. If the dispersion of the positional information obtained from the index area is larger than a preset value, remove positional information that deviates from a predetermined range and calculate the off-track amount of the track. An index servo method that positions the magnetic head based on the amount of off-track. (2) Each of the servo information is composed of a synchronization section, an erasing section, a synchronization section, and a position information section, and the period thereof is the charging time of the circuit that peak-holds the position information, and the peak-held position information. 2. The index servo method according to claim 1, wherein the index servo method is embedded so as to take a longer time than the sum of the time required for D conversion and import into the microprocessor. (3) The index servo method according to claim 1 or 2, wherein the position information is comprised of a dibit pattern. (4) The index servo method according to claim 1, wherein the servo information is written in accordance with an index signal synchronized with a motor that rotates the magnetic disk. (5) The positioning of the magnetic head is performed by a stepper motor, and the positioning of the magnetic head is performed by controlling current flowing through the A phase and B phase of the stepper motor with a microprocessor via a D/A converter. An index servo system according to claim 1, characterized in that: